You Slot Right Into My Life
by allwalkfree
Summary: The Journey of Zenitsu and how he managed, without trying, to win over Obanai Iguro, and become the snake Pillar's unofficial baby brother.
1. Chapter 1

Obanai knows disappointment, had dealt with disappointment all his life.

That feeling of being too late, that feeling of warm blood between his fingers, that feeling of seeing crying, hopeless faces. Yes, Obanai knows disappointment. He has been disappointed with himself too many times to count and has been disappointed in others even more, so when Uzai declares loudly that he's done with demon hunting, and that he is considering retirement, he glares and calls him pathetic.

Yes, he is disappointed in Uzai, and he tells him so. "We can't afford to lose you," he sighs. "Stop being a child Uzai, Rengoku is dead. You're one of very fewer pillar's left."

Uzai runs his remaining hand through his hair and smiles sheepishly up at him; his wives not too far away, and a crying blonde teenager by his side. "I'm sorry Obanai," he says; grin a bit too sharp and eyes a bit too sad. "Me and my girls promised each other that we would retire after taking on an upper moon. We did, we won, and now I'm kinda done with all of this."

The snake pillar stares him down, but the sitting male's gaze is unwavering. Obanai sighs again. "You're pathetic," he finally mutters, turning away. "Love has never saved lives before."

He doesn't look back; walking away as fast and as quickly as possible, trying to not lose his cool, but he does hear the kid. The blonde, sniveling, pathetic kid.

"I don't know what his deal is Uzai-senpai," the brat blubbers. "But there is nothing wrong with picking love over fighting a war which you have given so much for already." There is a particular note In his voice that almost makes the snake pillar stop in his track and look back, but he refrains. Jumping down the roof instead, with only Uzai's happy cries of "you called me senpai you little brat," ringing in his ears and a certain pink haired girl dancing behind his eyes. 

* * *

He doesn't think much about the kid, not until he sees him next, sneaking out of the butterfly estate; hand clutched around his mid and face too bruised to be identifiable. If it wasn't for his hair, Ubanai wouldn't have even recognized him. He speaks up before the kid is fully out of view. "What are you doing out of bed?"

The brat jumps, and then visible curls in on himself with pain. "Ouch, ouch, ouch," he mutters; face pinched and eyes watering.

Obanai isn't sorry. "I said," he repeats himself. "What are you doing out of bed?" He has to speak a little louder than he likes; the estate running unusually high in patients this time, but the kid does hear him, and slowly turns around; lips wobbly and eyes glassy.

He looks pathetic.

"Leaving?" the kid finally says; trying his hardest not to meet his eyes. Obanai scoffs.

"You're in no condition."

"I know that!" The teen is tilting from side to side now; face taking an interesting shade of green. "There are a lot of new patients right now, and they don't have enough beds and I don't wanna take up more room since I'm feeling better!"

The kid says all of this in one breath, before faltering and clutching at his stomach even harder. Obanai is acting before he can even think. Shoving the teen none too gently into a chair and running away and coming back quickly with a trash can; just in time for the idiot to spew his guts out. He grimaces, disgust written all over his face and under his bandages, but he still finds himself lifting a hesitant hand to rub gentle circles on the blonde's back. "Easy brat," he mutters. "Easy."

The kid eventually lets up, lifting his head from the basket, and while shivering uncontrollably pushes himself till he's leaning fully against the chair. Obanai silently hands him a wad of paper towels. The blonde whispers something, but the snake pillar doesn't care enough to listen, instead he signals over the first medical personal he sees and sharply directs them to take the moron back to bed. "Don't let me find him wandering around again," he snaps. The man pales, and so does the kid. Obanai walks away.

"Thank you," someone calls out from behind him. He doesn't stop, but maybe, just maybe his shoulders relax just the tiniest bit at the appreciation. 

* * *

"You're really kind Kanroji-senpai!"

Obanai comes to a halt. Someone else was already here? Who? Why? He frowns. Mitsuri tended to be too nice for her own good, and Obanai had found himself threatening people into behaving themselves several times throughout their years together as pillars, so whoever was cozying up to the girl better be prepared for hell when they left the pink haired woman's company, because-

"Thank you Zenitsu! You're really kind too!"

A loud; almost grating awkward laugh, and a soft "thank you."

Obanai's muscles untense.

The blonde, the blonde was named Zenitsu right? Why the hell did he even know that? His frown lines deepen, and he finds himself opening the door to the dining room a lot softer than he'd intended. But not before he hears the brat's next, heartfelt words.

"I wish I'd known you when I was a kid," he says. "You don't hate me or call me annoying," Obanai barely catches the bright smile on the blonde's face as he opens the door. "I wish you were my big sister!"

The love pillar brightens up so much, Obanai would have cringed back from the sheer force of her smile if he hadn't been so used to it. "I'll be your big sis!" she says, and the brat smiles back; equally as bright. Obanai pauses at the door, watching them. They look ridiculous. Mouth stuffed half with food, hair clashing in colors, and soft giggles making them choke every now and then on their dinner. They look ridiculous, but still-

The snake pillar finds that his mouth quirks up just the slightest bit at the corner as he watches them. 

* * *

Bullies.

That's Obanai's first thought, when he comes across the pitiful scene in front of him that morning. Bullies.

'_How the hell,' _he thinks; speeding up just a little bit._ 'Do we have bullies in this organization when people are dying off like flies every day.'_

And how the hell was Zenitsu showing up everywhere and anywhere around him lately. He sighs.

"Stop that guys," the blonde wails; jumping after his sword as the cannon fodders throw it back and forth above his head. Laughing scornfully with each other. "That's mine. Give it back!"

They of course didn't, and the stupid boy keeps on whining and wailing and occasionally screaming "Tanjiro."

Pathetic.

It was clear this wasn't the first time the bulling had taken place by the way the other boys seemed overly familiar with the idiot, but it was also clear this might have been the first time they've gotten him without his ridiculous bodyguard around, because-

"Tanjiro isn't here to save you now crybaby," one of them taunted; lifting the sword high in the air, prepared to throw it. "What you gonna do when I throw it into the trees up there?"

Zenitsu pauses momentarily at those words. "Go get it?" he mutters finally; fists rubbing at his eyes.

They laugh, and the kid smiles tentatively back at them, as if trying his hardest to fit in, and that-

That makes something ugly crawl up Obanai's gut and weight heavily on his shoulders. He growls, and with a speed too fast to detect, the sword is clutched between his fingers, and the cannon fodder his lying flat on the ground; his boot pressed on his back. "And pray tell," he says slowly; grinding his foot down and making the idiot gasp. "What Is going on here?"

"Nothing, nothing!" The morons scramble back, bumping into each other as they try their best to get away from his wrath. Doesn't really matter, because in a blink of an eye, he has them all lying on the floor, unconscious. Except for one, the brat.

Walking towards him, he notices while Zenitsu is visibly shaken, the kid doesn't move away from him, instead his eyes grow just a little bit lighter and his lips curl into a smile. "Thanks, Iguro-senpai," he says.

And Obanai just sighs. Handing over the sword carefully, and for some strange reason reaches out without thinking, and pats the kid's hair. The brat just blinks up at him owlishly. "Stop letting these idiots walk all over you," he grumbles, and then he's gone. 

* * *

Next time he sees the brat, he's called in for backup. Apparently two lower moons had been terrorizing the district some of the younger demon slayers had been sent to, and unfortunately, most of them had died.

It left a bitter taste in Obanai's mouth, as the sword pillar quickened his pace to get to the kids as fast as possible. According to his messenger crow, not many were left; barely hanging on.

How so many inexperienced children were still breathing was honestly a miracle, and if he wanted it to stay that way, Obanai needed to hurry.

Finally spotting the riverside, the pillar jumped up; landed on a tree branch and continued on. Already he could smell the blood, a stench of death so strong, he would have gagged if he'd been a lesser man.

'_I'm going to make them pay_' he thought furiously; clutching at his sword, he bounced from tree to tree, not allowing his eyes to linger any longer on the dead corpses splayed on the ground bellow him. And then-

The hair on the back of his neck raised; the air tasted differently, and suddenly – Lightning flashed across the sky.

Obanai breathed.

"Zenitsu."

The energy dancing around the clouds was brilliant, bright, breathtaking, and powerful. The snake pillar started moving again; eyes narrow and teeth gritted tight. He'd heard about the kid's powers from Uzai. And of course, he hadn't believed him, not really. The other pillar had no reason to lie to him, but, how could someone so pathetic, be so powerful?

Still, that was him, without a doubt, and-

He needed him.

The enemy were two lower moons sure, but the kid wasn't a pillar, and he wasn't; as difficult as it was to admit, that moron Tanjiro, so he couldn't, he wouldn't be able to fend them off for long, not without help, and with that in mind-

Obanai Iguro jumped down to ground level and found his eyes zeroing on the only standing figure through the plethora of scattered bodies.

The blonde teenager was currently standing still, body unmoving and eyes; his eyes were closed.

There were no holes in his stance, and surrounded on both sides by two agitated demons, the kid, remained unfazed.

Behind him were seven up to ten other slayers; curled up and scared. They were still holding their broken swords between bloodied fingers, but it was clear none of them seemed up to the task. None of them had the kids back, and-

The snake pillar immediately recognized at least two of them from the week before. The bullies. He almost snorted at the irony.

Pathetic.

He grabbed his sword then, and is only a second away from unsheathing it, when – The kid moves. _'Fast,' _is his first thought. _'The kid's fast.'_

The demon snaps out of the way, but before it could get its footing under it, Zenitsu is behind it; eyes still shut, but blade slicing through its head with elegance meant for the seeing. The other demon takes that very opportunity, it most likely created for itself to attack, but Obanai was tired of just standing around, and with a split-second notice, another head rolls off the neck of a body.

Obanai pushes himself back to his full height, flicking the remaining blood off his blade, before he turns around to look at the kid. "Zenitsu?"

No answer.

Instead, the kid tilts sideways and falls into the pillar's waiting arms. Sighing, Obanai looked down at the blonde's head pressed up against his chest.

What an interesting brat.

"Rest," he said finally; fingers coming up to pat the bloodied locks of the teen. "You did good."


	2. Chapter 2

Mizuchi had gone missing. Obanai knew that the snake liked to do things the way he wanted to, but at this particular time of the year, the man wasn't very comfortable leaving his friend wandering around in the chilling weather. It wasn't good for him, and Obanai rather keep him folded tight under his uniform instead of having the fool out and about in the cold.

So, with a newfound worry slithering through his veins, the snake pillar made a quick work of the entire training facility. It shouldn't be too hard to find his friend, but alas, after searching from dust to dawn; occasionally being called off to supervise some idiots, Obanai was rightfully exhausted.

"Stupid snake," he grumbled; looking once more under his closet and around his desk. "If you die, I won't mourn you."

Still, few people or creatures in this entire world made the snake pillar worried, and unfortunately, Mizuchi was on that list, so with another exasperated sigh, the demon slayer pushed his window open and jumped down to the garden bellow.

'_One last time,' _he told himself, scouring the only ground he hadn't covered fully yet. 'One_ last time and then that stupid snake can kindly die out there.' _

That's - That's when he found him, or specifically, that's when he found _them. _

A very familiar; by this point, blonde was leaning against the old tree by the fourth training ground, haori folded delicately in his arms; close to his chest, and a white snake head popping up from all the clothing material.

For a second, he couldn't move.

It was such a strange sight. Mizuchi; who didn't particularly like anyone else, besides kanroji, and previously Rengoku; was now comfortably resting his head against the arm of the only crybaby demon slayer Obanai knew.

It was such an unusual sight. And not only that, because if he tilted his head just so, and tried to listen, he could hear the soft murmurs of the blonde, as the kid apparently held a very animate, one sided conversation with Mizuchi.

Obanai blinked.

Huh?

He just stood there for a while, watching silently as Zenitsu said something; a slight frown twisting the blonde's face into a look of concern, before the kid reached out a shaking hand, and brushed a gentle finger across the snake's head. To Obanai's surprise,

Mizuchi did nothing more than lean up against the touch, making the kid brighten up with a smile of utter affection.

It was all so surreal.

Contemplating for a minute, the snake pillar finally just shook his head, turned back towards where he came, and vanished behind the wooden trees.

Mizuchi would find him again when he'd had enough of being pampered.

XXXXXX

He's eating a bowl of curry when he sees the brat again.

The kid is looking this way and that from the entrance to the mess hall. Clearly his friends where nowhere to be found, and the idiot didn't know what to do with himself without them.

Pathetic.

Still; Obanai lifted the next bite to his lips and chewed thoughtfully. Kanroji had told him once; quite vibrantly and with the largest smile across her mouth that Zenitsu-chan also liked this type of curry!

He hadn't really cared, but-

Looking back up at the still nervous kid, he sighed.

Raising a single arm up in the air, he waved the brat over when their eyes finally met. He wasn't about to scream across the dining hall, so with a swift motion of his hand in his direction, he put his arm down, and started eating again. He didn't lift his head until the orange and yellow haori was coloring his vision.

"Iguro-senpai?"

He stared up at the kid. The blonde flinching back slightly at the piercing gaze, but mostly held his ground. Obanai's lips quirked up, and the kid's eyes zeroed in on the motion; probably shocked that the snake pillar's face wasn't covered by bandages this time.

He didn't let the kid get another word in though, instead opting to shove his second bowl of curry in the teen's direction.

"Sit," he said. "Eat."

Watery eyes and a distressed but hopeful smile was his answer.

Obanai snorted. "You're gonna be the death of me brat."

XXXXXX

Obanai couldn't breathe.

His chest was burning, his lungs felt too constricted, and his face; his face felt like it'd been set on fire. Gasping softly, he tried and failed to turn his body enough so that he could press his cheek against the colder side of his pillow.

Pathetic.

He was pathetic.

How could a sword's man of his caliber fall to something as weak as a fever? The world was crumbling right under the demon slayer corps and here he was, lying in a fucking hospital bed, dying of a fever.

Clenching his eyes shut, he felt his cheeks heatup even more, not from his sickness this time, but from the sheer humiliation of sharing these courters with lesser slayers. Slayers that unlike him actually had legitimate injuries.

Currently, he didn't even have the same respect as those cannon fodders, ranked so much lower than him.

How humiliating, how pitiful. Obanai just wanted to disappear.

But then-

Something cold, something soothing, was being pressed against his burning forehead. It covered every inch of his warm skin, and made quick work of the flames licking under his very being. Obanai's lips parted in a sigh of relief. Finally – It didn't do much, but from the little it managed to dull his pain, the snake pillar was eternally grateful.

"Is that better Senpai?" Uncertain, worried, scared.

_Zenitsu . _

Of course, it was the brat. At this point, Obanai was sure the kid had some gravitational pull in his direction.

"Senpai?"

He didn't say anything. The brat sounded scared and his voice was quivering to a point where Obanai was concerned he would burst out in tears anytime now, but – He didn't say anything.

Not that he didn't want to, but because he couldn't.

His lips wouldn't move, sound wouldn't form passed soft gurgles and although he wanted to a peace the brat to a degree, he simply, just couldn't. Instead-

Moving his fingers carefully, slowly; he reached out, and; fumbling slightly, he grabbed the younger's forearm, and squeezed.

The worried murmuring above him paused, and gently, oh so gently, cold fingers came up to cover his own hand and didn't let go.

"I'm here senpai," Zenitsu said. "I'm here now, so please rest."

Obanai wasn't a sentimental fool, he didn't care much for people, and he cared even less for people not on the same rank as him, but-

Tears trailed down passed his ears and dripped softly against his pillow. Eyes closed, he couldn't make out the kid's expression, but – tightening his own grip, he tried and maybe didn't fail this time to send the kid the tiniest of smiles. "Thanks, Zenitsu," he mouthed.

He wasn't sure if the brat got what he was trying to say, wasn't sure if his lips actually moved rather than his imagination playing tricks on him, but; hand came up to wipe at his cheeks.

"You're welcome senpai."

He breathed, his chest didn't burn as much, and his face didn't hurt where the hand rested against it, so he breathed, and finally – finally, was drawn back into the dreamland he hadn't been able to visit all this time.

Blissful darkness, and the gentle light of a soft hand against his cheek.

Safe, he was safe.

XXXXXX

Tanjiro Kamado, he really hated Tanjiro Kamado.

Sitting on the cold floor across from the problem child, Obanai could do nothing more than glare furiously at the smiling boy in front of him.

"Stop that," he snapped. The idiot blinked, confused.

"Stop what Iguro-san?"

Obanai's glare turned even more fierce. "Stop acting like you know him better than me."

Now the kid looked really confused, but Obanai hadn't been a pillar for this long, to fall for a measly, pathetic act like that. The problem child knew very well what he was talking about.

"What are you talking about?"

Well, apparently not.

The snake pillar scowled. Almost ready to rise from his seat, when a gentle hand was placed on his elbow, holding him down.

"Can we not, senpai?" Zenitsu pleaded; looking just as clueless as Kamado Tanjiro, while still managing to bring out the puppy-dog eyes. "Tanjiro is my best friend, and I want you two to get along."

"That's impossible," he said, at the same time as the other brat shimmed up brightly.

"Sure, no problem Zenitsu!"

He growled, and the blonde tightened his grip even more. "Please senpai?"

Obanai's muscles were still tense; getting even more infuriated by the look of slight amusement on the problem child's face, but-

Zenitsu didn't ask him for much, if at all, so – He could do this one thing for him. Just this once. Still,

Lifting a finger in warning, he pointed it straight at the smiling teen in front of him. "Listen carefully, Kamado Tanjiro," he hissed. "For the last time, Zenitsu doesn't like sushi!"

Tanjiro pouted at him, and Zenitsu sighed.

Obanai didn't care. No way was he gonna let the moron eat something that was just gonna make him throw up later. Kamado Tanjiro could kindly keep his fucking dinner to himself.

"How does he know he doesn't like it, if he doesn't try?" the idiot had the nerve to ask, and well, that was the snake pillar's last straw.

Before he knew it, he was grabbing for the moron's throat and Zenitsu was screaming frantically as he threw himself around his waist, while the problem child had jumped out of the way; eyes wide.

Safe to say, the mess hall descended into utter chaos, with food flying everywhere and people screaming and ducking for cover.

And – Obanai never lived that mess down.

No one would ever let him forget the hilarious spectacle that he made that day, ever.

Obanai hated Tanjiro Kamado. He really really hated Tanjiro Kamado.

XXXXXX

Zenitsu's sword missed him by a hair; skimming the side of his neck, as the teenager tried his best to keep up with the snake pillar's rapid motions.

"Too slow, Zenitsu," Obanai snapped; slamming the flat end of his sword behind the other's knee, making the brat's legs buckle. "Concentrate!"

Nodding, the kid took up a familiar stance; feet spread apart, and arms folded in front of him, sword held steady. Obanai tilted his chin in approval, before pouncing again.

They went like that, back and forth for the duration of the evening; the kid hitting the ground with a painful thud every other second, but Obanai didn't relent.

"Get up brat," he said, pointing the sharp end at Zenitsu's eye. "Get up and fight."

This time however, the kid looked away; fists clenched at the material of his pants, and lips biting hard, on his lip. "I can't senpai," he whispered; voice breaking at the top. "I'm just no good."

"That's no way to face the world. Get up."

Obanai had no time for weaklings with even weaker mindset, besides - "You're better than you think Zenitsu, so ."

The blonde's head shot up.

He looked disbelieving, confused, and maybe, just maybe, slightly bit hopeful.

The snake pillar sighed; dropping down on his own knees too, folding his legs under him, so he could be on eye level with the brat. "Want to tell me what's going on?"

The teen didn't meet his gaze. But eventually-

"I got a message back from Kaigaku-senpai, and he said somethings that made me think."

"Kaigaku?"

The kid nodded once. "Yeah, he's my senpai. He was taught by gramps too. The breath of thunder style."

Obanai frowned. "And what did he say to you?"

The kid grimaced. "He said," taking a calming breath, he tried again. "He said that I won't amount to much. I don't know anything beside the first breath, so I guess he's right."

He looked heartbroken as he admitted the fact. Sad, unsure – Insecure

Obanai didn't like it. "Where is your senpai now?" The kid shrugged.

"I don't know."

"Exactly."

Zenitsu blinked at him. "What do you mean?"

The snake pillar huffed in exasperation. "I mean that he isn't here, you are. That says a lot about how far you've come, brat. Don't let the asshole get to you."

It took a second for the words to fully dawn on the kid, but when they did-

"Thank you senpai!" He cried; suddenly throwing himself at the older male and crying dramatically into his shoulder.

Obanai wanted to fling him away, but-

Just this once, just this one time, he would let him do what he wanted.

If a tiny voice in the back of his mind said, 'You_ always let him do what he wants,' _well, that wasn't anyone else's business now was it.

They are all fighting for their lives. Time is running out, pillars are scattered, Muzan might get away, ubuyashiki-sama is dead, and-

They couldn't lose this fight, they couldn't die, he couldn't let Kanroji die, they couldn't let humanity down.

Victory. Victory was none negotiable.

It was do or die, and Obanai didn't have time to think about anyone else outside of his and Kanroji's immediate survival and victory, but-

When his crow screeches at the top of its lung that the sixth upper moon is dead, that one Kaigaku is dead. Killed by the thunder breath user, one zenitsu agatsuma, Obanai can't help but grin wider than he'd ever grinned before, because, fuck that loser. Zenitsu was twice the demon slayer that man would and could ever be.

Meeting Kanroji's eyes briefly, they share a brief smile; a proud smile.

Because, things might be looking bleak right now, they might be grieving one of their biggest losses, but, maybe when everything was said and done with, they could take Zenitsu out for ice cream.

"Chocolate chip?" Kanroji calls out, dropping down and swinging her sword at the head of the demon.

Obanai snorts. "Hell no," he says. "strawberry is the only answer."

* * *

First, just wanna say that I have no clue if Obanai's snake actually has a name. If he does, feel free to tell me so I can change the name to its original one. I chose to call him Mizuchi, because my dumbass self actually looked up japanese snake names and found this one. It says (The Mizuchi (大虬, 蛟龍、蛟, 美都知) is a type of Japanese dragon or legendary serpent-like creature, either found in aquatic habitat or otherwise connected to water) so hey, fits well enough so that's what happened.


End file.
